RFC 6130

Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)

5. Protocol Parameters and Constants
The parameters and constants used in this specification are described
in this section.
5.1. Protocol and Port Numbers
This protocol specifies HELLO messages, which are included in packets
as defined by [RFC5444]. These packets may be sent using either the
"manet" protocol number or the "manet" well-known UDP port number, as
specified in [RFC5498].
5.2. Multicast Address
This protocol specifies HELLO messages, which are included in packets
as defined by [RFC5444]. These packets may be locally transmitted
using the link-local multicast address "LL-MANET-Routers", as
specified in [RFC5498].
5.3. Interface Parameters
The interface parameters used by this specification may be classified
into the following four categories:
o Message intervals
o Information validity times
o Link quality

o Jitter
These are detailed in the following sections.
Different MANET interfaces (on the same or on different routers) MAY
employ different interface parameter values and MAY change their
interface parameter values dynamically, subject to the constraints
given in this section. A particular case is where all MANET
interfaces on all MANET routers within a given MANET employ the same
set of interface parameter values.
5.3.1. Message Intervals
HELLO messages serve two principal functions:
o To advertise network addresses of this router's interface to its
1-hop neighbors. The frequency of these advertisements is
regulated by the interface parameters HELLO_INTERVAL and
HELLO_MIN_INTERVAL.
o To advertise this router's knowledge of each of its 1-hop
neighbors. The frequency of the advertisement of each such
neighbor is regulated by the interface parameter REFRESH_INTERVAL.
Specifically, these parameters are as follows:
HELLO_INTERVAL:
The maximum time between the transmission of two successive HELLO
messages on this MANET interface. If using periodic transmission
of HELLO messages, these SHOULD be at a separation of
HELLO_INTERVAL, possibly modified by jitter as specified in
[RFC5148].
HELLO_MIN_INTERVAL:
The minimum interval between transmission of two successive HELLO
messages on this MANET interface. (This minimum interval MAY be
modified by jitter, as defined in [RFC5148].)
REFRESH_INTERVAL:
The maximum interval between advertisements, in a HELLO message on
this MANET interface, of each 1-hop neighbor network address and
its status. In all intervals of length REFRESH_INTERVAL, a router
MUST include each 1-hop neighbor network address and its status in
at least one HELLO message on this MANET interface. (This may be
in the same or in different HELLO messages.)

REFRESH_INTERVAL thus represents the frequency at which a piece of
information, as received in HELLO messages, can be expected to be
refreshed. Thus, the REFRESH_INTERVAL is used as a basis for
determining when such information expires in receiving routers (see
Section 5.3.2). HELLO_INTERVAL represents the frequency of HELLO
message emissions. Logically, HELLO_INTERVAL cannot be greater than
the REFRESH_INTERVAL; otherwise, information cannot be refreshed in a
timely manner.
HELLO messages can, however, be sent with a higher frequency. A
possible use for sending HELLO messages at such a higher frequency
includes sending partial HELLO messages (e.g., accommodating
constraints on packet sizes from the underlying medium) refreshing
only part of the information in each HELLO message. Another use is
for a router to send "empty HELLO messages", advertising its own
presence frequently in smaller HELLO messages (e.g., in case HELLO
message exchange success rates are used for link quality estimation,
or to enable rapid detection by new routers in the neighborhood) in
between HELLO messages refreshing neighbor information in other
routers.
The following constraints apply to these interface parameters:
o HELLO_INTERVAL > 0
o HELLO_MIN_INTERVAL >= 0
o HELLO_INTERVAL >= HELLO_MIN_INTERVAL
o REFRESH_INTERVAL >= HELLO_INTERVAL
o If an INTERVAL_TIME Message TLV as defined in [RFC5497] is
included in a HELLO message, then HELLO_INTERVAL MUST be
representable as described in [RFC5497].
If REFRESH_INTERVAL > HELLO_INTERVAL, then a router may distribute
its neighbor advertisements between HELLO messages in any manner,
subject to the constraints above.
In the absence of any changes to the local neighborhood, a router
will send a HELLO message on a MANET interface after an (possibly
jittered) interval of length HELLO_INTERVAL. For a router to employ
this protocol in a purely responsive manner on a MANET interface,
i.e., for the router to only send HELLO messages on that MANET
interface as a response to external events, HELLO_INTERVAL (and hence
also REFRESH_INTERVAL) SHOULD be set sufficiently large, i.e., such
that a responsive HELLO message is always expected with a shorter
period than this value.

If a router has more than one MANET interface, then, even if the
router configures different values of HELLO_INTERVAL on each MANET
interface, the router SHOULD configure the same value of
HELLO_MIN_INTERVAL on all MANET interfaces on which responsive HELLO
messages may be sent. (This ensures that changes observed on one
MANET interface are reported on other MANET interfaces, so that 1-hop
neighbors connected to the latter can maintain up-to-date 2-hop
neighborhood information.)
5.3.2. Information Validity Times
The following interface parameters manage the validity time of link
information:
L_HOLD_TIME:
The period of advertisement, on this MANET interface, of former
1-hop neighbor network addresses as lost in HELLO messages,
allowing recipients of these HELLO messages to accelerate removal
of this information from their Link Sets. L_HOLD_TIME MAY be set
to zero, if accelerated information removal is not required.
H_HOLD_TIME:
Used as the Value in the VALIDITY_TIME Message TLV included in all
HELLO messages on this MANET interface. It is then used by each
router receiving such a HELLO message to indicate the validity of
the information taken from that HELLO message and recorded in the
receiving router's Information Bases.
Note that as each item of neighbor information is included in HELLO
messages within an interval of length REFRESH_INTERVAL, constraints
on H_HOLD_TIME are based on REFRESH_INTERVAL, not on HELLO_INTERVAL.
The following constraints apply to these interface parameters:
o L_HOLD_TIME >= 0
o H_HOLD_TIME >= REFRESH_INTERVAL
o If HELLO messages can be lost, then both parameters SHOULD be
significantly greater than REFRESH_INTERVAL.
o H_HOLD_TIME MUST be representable as described in [RFC5497].

5.3.3. Link Quality
The following interface parameters manage the usage of link quality
(see Section 14):
HYST_ACCEPT:
The link quality threshold at or above which a link becomes
usable, if it was not already so.
HYST_REJECT:
The link quality threshold below which a link becomes unusable, if
it was not already so.
INITIAL_QUALITY:
The initial quality of a newly identified link.
INITIAL_PENDING:
If true, then a newly identified link is considered pending, and
is not usable until the link quality has reached or exceeded the
HYST_ACCEPT threshold.
The following constraints apply to these interface parameters:
o 0 <= HYST_REJECT <= HYST_ACCEPT <= 1
o 0 <= INITIAL_QUALITY <= 1.
o If link quality is not updated, then INITIAL_QUALITY >=
HYST_ACCEPT.
o If INITIAL_QUALITY >= HYST_ACCEPT, then INITIAL_PENDING := false.
o If INITIAL_QUALITY < HYST_REJECT, then INITIAL_PENDING := true.
5.3.4. Jitter
If jitter, as defined in [RFC5148], is used, then these parameters
are as follows:
HP_MAXJITTER:
Represents the value of MAXJITTER used in [RFC5148] for
periodically generated HELLO messages on this MANET interface.
HT_MAXJITTER:
Represents the value of MAXJITTER used in [RFC5148] for externally
triggered HELLO messages on this MANET interface.
For constraints on these interface parameters, see [RFC5148].

5.4. Router Parameters
The two router parameters defined by this specification are in the
category of information validity time.
5.4.1. Information Validity Time
The following router parameter manages the validity time of lost
symmetric 1-hop neighbor information:
N_HOLD_TIME:
Used as the period during which former 1-hop neighbor network
addresses are advertised as lost in HELLO messages, allowing
recipients of these HELLO messages to accelerate removal of this
information from their 2-Hop Sets. N_HOLD_TIME MAY be set to
zero, if accelerated information removal is not required.
I_HOLD_TIME:
The period for which a recently used local interface network
address is recorded.
The following constraints apply to these router parameters:
o N_HOLD_TIME >= 0
o I_HOLD_TIME >= 0
5.5. Parameter Change Constraints
If protocol parameters are changed dynamically, the constraints in
this section apply.
HELLO_INTERVAL
o If the HELLO_INTERVAL for a MANET interface increases, then the
next HELLO message on this MANET interface MUST be generated
according to the previous, shorter, HELLO_INTERVAL. A number
of subsequent HELLO messages MAY be generated according to the
previous, shorter, HELLO_INTERVAL (but MUST include times
according to current parameters). This ensures that "promises"
as to timely transmission of a future HELLO message are kept
until these previous promises have expired.
o If the HELLO_INTERVAL for a MANET interface decreases, then the
following HELLO messages on this MANET interface MUST be
generated according to this current, shorter, HELLO_INTERVAL.

REFRESH_INTERVAL
o If the REFRESH_INTERVAL for a MANET interface increases, then
the content of subsequent HELLO messages must be organized such
that the specification of the old value of REFRESH_INTERVAL is
satisfied for a further period equal to the old value of
REFRESH_INTERVAL.
o If the REFRESH_INTERVAL for a MANET interface decreases, then
it MAY be necessary to reschedule HELLO message generation on
that MANET interface, in order for the specification of
REFRESH_INTERVAL is satisfied from the time of change.
HYST_ACCEPT and HYST_REJECT
o If HYST_ACCEPT or HYST_REJECT changes, then the appropriate
actions for link quality change, as specified in Section 14.3,
MUST be taken.
L_HOLD_TIME
o If L_HOLD_TIME changes, then the expiry times of all relevant
Link Tuples MUST be changed.
N_HOLD_TIME
o If N_HOLD_TIME changes, then the expiry times of all relevant
Lost Neighbor Tuples MUST be changed.
HP_MAXJITTER
o If HP_MAXJITTER changes, then the periodic HELLO message
schedule on this MANET interface MAY be changed.
HT_MAXJITTER
o If HT_MAXJITTER changes, then externally triggered HELLO
messages on this MANET interface MAY be rescheduled.
5.6. Constants
The constant C (time granularity) is used as specified in [RFC5497].
6. Local Information Base
A router maintains a Local Information Base that records information
about its interfaces (MANET and non-MANET). Each interface of a
router MUST be identified by at least one network address. Such

network addresses MAY be specific to that interface, or MAY in some
circumstances be used by more than one interface as specified below.
The Local Information Base is not modified by signaling. If a
router's interface configuration changes, then the Local Information
Base MUST reflect these changes. This MAY also result in signaling
to advertise these changes.
It is not necessary to include all addresses of an interface in the
Local Information Base, and hence in HELLO messages. However, any
address that may be the source address of an IP datagram sent from
that interface MUST be included (and at least one address MUST be
included). A protocol using this specification MAY add additional
requirements to these, e.g., that any address that may be the
destination address of an IP datagram is also included.
The addresses assigned to an interface are "owned" by the router, and
MUST NOT be used by any other router as an interface address. If an
address has a prefix length and represents a range of addresses, this
applies to all addresses in that range (i.e., such ranges MUST NOT
overlap).
The addresses assigned to different interfaces on the same router
MUST be distinct (hence, network address ranges MUST NOT overlap)
except that:
o The same address MAY be assigned to any number of non-MANET
interfaces as well as to one (or more if the following condition
also applies) MANET interface.
o The same address MAY be assigned to two (or more if each pair
satisfies this condition) MANET interfaces if those two MANET
interfaces cannot communicate to, from, or one to and one from any
other MANET interface of another router.
6.1. Local Interface Set
A router's Local Interface Set records its local interfaces. It
consists of Local Interface Tuples, one per interface:
(I_local_iface_addr_list, I_manet)
where:
I_local_iface_addr_list is an unordered list of the network
addresses of this interface.

I_manet is a boolean flag, describing if this interface is a MANET
interface.
Local Interface Tuples are removed from the Local Interface Set only
when the routers' interface configuration changes, subject to
Section 9, i.e., they are not subject to timer-based expiration.
6.2. Removed Interface Address Set
A router's Removed Interface Address Set records network addresses
that were recently used as local interface network addresses. If a
router's interface network addresses are immutable, then the Removed
Interface Address Set is always empty and MAY be omitted. It
consists of Removed Interface Address Tuples, one per network
address:
(IR_local_iface_addr, IR_time)
where:
IR_local_iface_addr is a recently used network address of an
interface of this router.
IR_time specifies when this Tuple expires and MUST be removed.
7. Interface Information Bases
A router maintains an Interface Information Base for each of its
MANET interfaces. This records information about links to that MANET
interface and symmetric 2-hop neighbors that can be reached in two
hops using those links as the first hop. Each Interface Information
Base includes a Link Set and a 2-Hop Set.
A network address of a symmetric 2-hop neighbor can also be present
as the network address of a 1-hop neighbor. This allows the router
using this network address to be immediately considered as a
symmetric 2-hop neighbor if it fails to be a symmetric 1-hop
neighbor.
An element that specifies a time is considered expired if the current
time is greater than or equal to that time. One such element,
present in most Tuples, indicates, when expired, that the Tuple
itself is considered expired and MUST be removed. Tuples that do not
have such a time element are removed at other times as specified; for
example, a Neighbor Tuple is removed when all corresponding Link
Tuples have been removed.

7.1. Link Set
An interface's Link Set records links from other routers that are, or
recently were, 1-hop neighbors. It consists of Link Tuples, each
representing a single link:
(L_neighbor_iface_addr_list, L_HEARD_time, L_SYM_time,
L_quality, L_pending, L_lost, L_time)
where:
L_neighbor_iface_addr_list is an unordered list of the network
addresses of the MANET interface of the 1-hop neighbor;
L_HEARD_time is the time up to which the MANET interface of the
1-hop neighbor would be considered heard if not considering link
quality;
L_SYM_time is the time up to which the link to the 1-hop neighbor
would be considered symmetric if not considering link quality;
L_quality is a dimensionless number between 0 (inclusive) and 1
(inclusive) describing the quality of a link; a greater value of
L_quality indicating a higher quality link;
L_pending is a boolean flag, describing if a link is considered
pending (i.e., a candidate, but not yet established, link);
L_lost is a boolean flag, describing if a link is considered lost
due to low link quality;
L_time specifies when this Tuple expires and MUST be removed.
The status of the link, as obtained through HELLO message exchange
and using link quality, is denoted L_status. L_status can take the
Values PENDING, HEARD, SYMMETRIC, and LOST. The values LOST,
SYMMETRIC, and HEARD are defined in Section 18.5. The Value PENDING
is never used in a HELLO message, it is only used locally by a
router, and any Value distinct from LOST, SYMMETRIC, and HEARD may be
used.
L_status is defined by:
1. If L_pending = true, then L_status := PENDING;
2. otherwise, if L_lost = true, then L_status := LOST;

3. otherwise, if L_SYM_time is not expired, then L_status :=
SYMMETRIC;
4. otherwise, if L_HEARD_time is not expired, then L_status :=
HEARD;
5. otherwise, L_status := LOST.
7.2. 2-Hop Set
An interface's 2-Hop Set records network addresses of symmetric 2-hop
neighbors, and the symmetric links to symmetric 1-hop neighbors
through which these symmetric 2-hop neighbors can be reached. It
consists of 2-Hop Tuples, each representing a single network address
of a symmetric 2-hop neighbor, and a single MANET interface of a
symmetric 1-hop neighbor.
(N2_neighbor_iface_addr_list, N2_2hop_addr, N2_time)
where:
N2_neighbor_iface_addr_list is an unordered list of the network
addresses of the MANET interface of the symmetric 1-hop neighbor
from which this information was received;
N2_2hop_addr is a network address of a symmetric 2-hop neighbor
that has a symmetric link (using any MANET interface) to the
indicated symmetric 1-hop neighbor;
N2_time specifies when this Tuple expires and MUST be removed.
8. Neighbor Information Base
Each router maintains a Neighbor Information Base that records
information about network addresses of current and recently symmetric
1-hop neighbors.
8.1. Neighbor Set
A router's Neighbor Set records all network addresses of each 1-hop
neighbor. It consists of Neighbor Tuples, each representing a single
1-hop neighbor:
(N_neighbor_addr_list, N_symmetric)

where:
N_neighbor_addr_list is an unordered list of the network addresses
of a 1-hop neighbor;
N_symmetric is a boolean flag, describing if this is a symmetric
1-hop neighbor.
Neighbor Tuples are removed from the Neighbor Set only when
corresponding Link Tuples expire from the routers' Link Set, i.e.,
Neighbor Tuples are not directly subject to timer-based expiration.
8.2. Lost Neighbor Set
A router's Lost Neighbor Set records network addresses of routers
that recently were symmetric 1-hop neighbors but that are now
advertised as lost. It consists of Lost Neighbor Tuples, each
representing a single such network address:
(NL_neighbor_addr, NL_time)
where:
NL_neighbor_addr is a network address of a router that recently
was a symmetric 1-hop neighbor of this router;
NL_time specifies when this Tuple expires and MUST be removed.
9. Local Information Base Changes
The Local Information Base MUST be updated in response to changes in
the router's local interface configuration. These MAY also change
the Interface Information Base and the Neighbor Information Base. If
any changes to the latter Information Bases satisfy any of the
conditions described in Section 13, then those changes MUST be
applied immediately, unless noted otherwise below.
A router MAY transmit HELLO messages in response to these changes.
9.1. Adding an Interface
If an interface is added to the router, then this is indicated by the
addition of a Local Interface Tuple to the Local Interface Set. If
the new interface is a MANET interface, then an initially empty
Interface Information Base MUST be created for this new MANET
interface. The actions in Section 9.3 MUST be taken for each network
address of this added interface. A HELLO message MAY be sent on all
MANET interfaces, it SHOULD be sent on the new interface if it is a

MANET interface. If using scheduled messages, then a message
schedule MUST be established on the new MANET interface.
9.2. Removing an Interface
If an interface is removed from the router, then this MUST result in
changes to the Local Information Base and to the Neighbor Information
Base as follows:
1. Identify the Local Interface Tuple that corresponds to the
interface to be removed.
2. For each network address (henceforth removed address) in the
I_local_iface_addr_list of that Local Interface Tuple, if that
network address is not in the I_local_iface_addr_list of any
other Local Interface Tuple, then create a Removed Interface
Address Tuple with:
o IR_local_iface_addr := removed address;
o IR_time := current time + I_HOLD_TIME.
3. Remove that Local Interface Tuple from the Local Interface Set.
4. If the interface to be removed is a MANET interface (i.e., with
I_manet = true), then:
1. Remove the Interface Information Base for that MANET
interface;
2. All Neighbor Tuples for which none of the network addresses
in its N_neighbor_addr_list are contained in any
L_neighbor_iface_addr_list in any remaining Link Tuple are
removed.
If the removed interface is the last MANET interface of the router,
then there will be no remaining Interface Information Bases, and the
router will no longer participate in this protocol.
After removing the interface and making these changes, a HELLO
message MAY be sent on all remaining MANET interfaces.
9.3. Adding a Network Address to an Interface
If a network address is added to an interface, then this is indicated
by the addition of a network address to the appropriate
I_local_iface_addr_list. The following changes MUST be made to the
Information Bases:

1. Remove any Removed Interface Address Tuple whose
IR_local_iface_addr is the added network address.
2. Remove any Neighbor Tuples whose N_neighbor_addr_list contains a
network address that overlaps the added network address.
3. Remove any Link Tuples, in any Link Set, for which either:
o L_neighbor_iface_addr_list contains any network address in the
N_neighbor_addr_list of any removed Neighbor Tuple; OR
o L_neighbor_iface_addr_list contains a network address that
overlaps the added network address.
Apply Section 13.2 but not Section 13.3.
4. Remove any Lost Neighbor Tuples whose NL_neighbor_addr overlaps
the added network address.
5. Remove any 2-Hop Tuples whose N2_2hop_addr overlaps the added
network address.
After adding the network address and making these changes, a HELLO
message MAY be sent on all MANET interfaces.
These changes, other than to the appropriate I_local_iface_addr_list,
are made in order to maintain consistency of the Information Bases.
Specifically, these changes remove any record of any use of this
network address by routers in the 1-hop neighborhood or in the
symmetric 2-hop neighborhood of this router.
9.4. Removing a Network Address from an Interface
If a network address (henceforth removed address) is removed from an
interface, then:
1. Identify the Local Interface Tuple that corresponds to the
removed address.
2. If this is the only network address of that interface (the only
network address in the corresponding I_local_iface_addr_list),
then remove that interface as specified in Section 9.2.
3. Otherwise:
1. Remove the removed address from this I_local_iface_addr_list.

2. If the removed address is not in the I_local_iface_addr_list
of any other Local Interface Tuple, then create a Removed
Interface Address Tuple with:
o IR_local_iface_addr := removed address;
o IR_time := current time + I_HOLD_TIME.
After removing the network address and making these changes, a HELLO
message MAY be sent on all MANET interfaces.
10. Packets and Messages
The packet and message format used by this protocol is defined in
[RFC5444], which is used with the following considerations:
o This protocol specifies one Message Type, the HELLO message.
o A HELLO message MAY use any combination of Message Header options
specified in [RFC5444].
o HELLO messages MUST NOT be forwarded, i.e., a <msg-hop-limit>, if
present, MUST have the value 1.
o HELLO messages MAY be included in multi-message packets as
specified in [RFC5444].
o Received HELLO messages MUST be parsed in accordance with
[RFC5444]. A HELLO message that is not in conformance with
[RFC5444] MUST be discarded without being processed. A HELLO
message can also be discarded without being processed for other
reasons, see Section 12.1.
o This protocol specifies three Address Block TLVs. It also uses
two Message TLVs defined in [RFC5497]. These five TLV Types are
all defined only with Type Extension = 0. TLVs of other types,
and of these types but without Type Extension = 0, are ignored by
this protocol. All references in this specification to, for
example, an Address Block TLV with Type = LINK_STATUS, are to be
considered as referring to an Address Block TLV with Type =
LINK_STATUS and Type Extension = 0.
10.1. HELLO Messages
A HELLO message MUST contain:
o Exactly one VALIDITY_TIME Message TLV as specified in [RFC5497],
representing H_HOLD_TIME for the transmitting MANET interface.

The options included in [RFC5497] for representing zero and
infinite times MUST NOT be used.
A HELLO message transmitted due to a periodic timer SHOULD contain,
and otherwise (i.e., transmitted for any other reason, in particular
in response to any Information Base changes) MAY contain:
o Exactly one INTERVAL_TIME Message TLV as specified in [RFC5497],
representing HELLO_INTERVAL for the transmitting MANET interface.
The options included in [RFC5497] for representing zero and
infinite times MUST NOT be used.
A HELLO message MAY contain:
o Other Message TLVs.
o One or more Address Blocks, each with an associated Address Block
TLV Block, which MAY contain other Address Block TLVs.
10.1.1. Address Blocks
All network addresses in a router's Local Interface Set (i.e., in any
I_local_iface_addr_list) MUST be represented as address objects (see
[RFC5444]), and included in the Address Blocks in all generated HELLO
messages, with the following permitted exception:
o If the MANET interface on which the HELLO message is to be sent
has a single address with maximum prefix length (i.e., /32 for
IPv4, /128 for IPv6), then that address MAY be omitted from being
included in any Address Block, provided that this address is
included as the sending address of the IP datagram in which the
HELLO message is included.
All network addresses of the router's interfaces included in any
Address Block(s) MUST be associated with an Address Block TLV with
Type = LOCAL_IF, as defined in Table 1.
+----------+---------+----------------------------------------------+
| Name | Value | Description |
| | Length | |
+----------+---------+----------------------------------------------+
| LOCAL_IF | 1 octet | Specifies that the network address is |
| | | associated with the MANET interface on which |
| | | the message was sent (THIS_IF) or another |
| | | interface of the sending router (OTHER_IF). |
+----------+---------+----------------------------------------------+
Table 1: LOCAL_IF TLV Definition

Address Blocks MAY contain current or recently lost 1-hop neighbors'
network addresses, represented as address objects (see [RFC5444]),
each of which is associated with one or both Address Block TLVs as
described in Table 2.
+--------------+---------+------------------------------------------+
| Name | Value | Description |
| | Length | |
+--------------+---------+------------------------------------------+
| LINK_STATUS | 1 octet | Specifies the status of the link from |
| | | the indicated network address and to the |
| | | MANET interface over which the HELLO |
| | | message is transmitted (LOST, SYMMETRIC, |
| | | or HEARD). |
| OTHER_NEIGHB | 1 octet | Specifies that the network address is |
| | | (SYMMETRIC) or was (LOST) of a MANET |
| | | interface of a symmetric 1-hop neighbor |
| | | of the router transmitting the HELLO |
| | | message. |
+--------------+---------+------------------------------------------+
Table 2: LINK_STATUS and OTHER_NEIGHB TLV Definition
An Address Block TLV with Type = LINK_STATUS and Value = SYMMETRIC or
Value = LOST also performs the function of an Address Block TLV with
Type = OTHER_NEIGHB and the same Value. Including the latter
associated with the same address object is discouraged for efficiency
reasons. If an Address Block TLV with Type = LINK_STATUS and Value =
SYMMETRIC is combined with an Address Block TLV with Type =
OTHER_NEIGHB and Value = LOST associated with the same address
object, then the latter MUST be ignored and SHOULD NOT be included.
See Appendix A.
Other network addresses MAY be represented as address objects (see
[RFC5444]) and included in Address Blocks, but MUST NOT be associated
with any of the Address Block TLVs specified in this specification.
11. HELLO Message Generation
Each MANET interface MUST generate HELLO messages according to the
specification in this section. HELLO messages are generated for each
MANET interface independently. HELLO message generation and
scheduling MUST be according to the interface parameters for that
MANET interface, and MAY be independent for each MANET interface or,
interface parameters permitting, MANET interfaces MAY use the same
schedule.

If transmitting periodic HELLO messages, then, following a HELLO
message transmission on a MANET interface, another HELLO message MUST
be transmitted on the same MANET interface after an interval not
greater than HELLO_INTERVAL. Two successive HELLO message
transmissions on the same MANET interface MUST be separated by at
least HELLO_MIN_INTERVAL, except as noted in Section 11.2.1.
11.1. HELLO Message Specification
HELLO messages are generated independently on each MANET interface.
All network addresses in any I_local_iface_addr_list MUST be
included, represented as address objects (see [RFC5444]), except
that:
o If the interface on which the HELLO message is to be sent has a
single address with maximum prefix length (i.e., /32 for IPv4,
/128 for IPv6), then that address MAY be omitted, provided that
this address is included as the sending address of the IP datagram
in which the HELLO message is included.
All such included address objects MUST be associated with an Address
Block TLV with Type := LOCAL_IF and Value according to the following:
o If the address object represents a network address of the sending
MANET interface, then Value := THIS_IF.
o Otherwise, Value := OTHER_IF.
If such a network address is included in more than one
I_local_iface_addr_list, then, for efficiency reasons, it is
encouraged that the corresponding address object is associated with
only one Value using an Address Block TLV with Type := LOCAL_IF; this
MUST be Value := THIS_IF if the address object represents a network
address of the sending MANET interface.
The following network addresses of current or former 1-hop neighbors
MAY be represented as address objects (see [RFC5444]) and included in
any HELLO message, respecting the parameter REFRESH_INTERVAL for each
association for that MANET interface, and according to the following:
o Network addresses of MANET interfaces of 1-hop neighbors from the
Link Set of the Interface Information Base for this MANET
interface (i.e., from an L_neighbor_iface_addr_list), other than
those from Link Tuples with L_status = PENDING.

o Other network addresses of symmetric 1-hop neighbors from the
Neighbor Set of this router's Neighbor Information Base (i.e.,
from an N_neighbor_addr_list).
o Network addresses of MANET interfaces of previously symmetric or
heard 1-hop neighbors connected on this MANET interface from the
Link Set of the Interface Information Base for this MANET
interface (i.e., from an L_neighbor_iface_addr_list with L_status
= LOST).
o Other network addresses of previously symmetric 1-hop neighbors
from the Lost Neighbor Set of this router's Neighbor Information
Base (i.e., from an NL_neighbor_addr).
Each such address object (see [RFC5444]) MUST be associated with one
or more appropriate Address Block TLVs. Specifically:
1. For each address object (henceforth linked address) that
represents a network address contained in an
L_neighbor_iface_addr_list of a Link Tuple in the Link Set for
this MANET interface, for which L_status != PENDING, include the
linked address with an associated Address Block TLV with:
o Type := LINK_STATUS; AND
o Value := L_status.
2. For each address object (henceforth neighbor address) that
represents a network address contained in an N_neighbor_addr_list
in a Neighbor Tuple with N_symmetric = true and that has not
already been included with an associated Address Block TLV with
Type = LINK_STATUS and Value = SYMMETRIC, include the neighbor
network address with an associated Address Block TLV with:
o Type := OTHER_NEIGHB; AND
o Value := SYMMETRIC.
3. For each Lost Neighbor Tuple whose NL_neighbor_addr (henceforth
lost address) has not already been represented as an address
object and included, include lost address with an associated
Address Block TLV with:
o Type := OTHER_NEIGHB; AND
o Value := LOST.

If any such network addresses have been added to these Information
Bases since the last HELLO message was sent on this MANET interface,
or if their status (as indicated by these TLVs and the Values they
associate with that network address) have changed since that network
address was last reported on this MANET interface, then that network
address, and the indicated TLVs, SHOULD be included in the HELLO
message.
If the address object (see [RFC5444]) representing a network address
of a 1-hop neighbor is specified with more than one associated
Address Block TLV, then these Address Block TLVs MAY be independently
included or excluded from each HELLO message. Each such Address
Block TLV MUST be included associated with the address object
representation of that network address in a HELLO message sent on
that MANET interface in every interval of length equal to that MANET
interface's parameter REFRESH_INTERVAL. Address Block TLVs
associated with the same address object included in the same HELLO
message MAY be applied to the same or different copies of that
address object.
An implementation of this protocol MAY limit the information included
in each HELLO message, for example, to accommodate smaller MTU sizes.
HELLO messages remain constrained by the above requirements, in
particular, that all local interface information MUST be included in
all HELLO messages, and that all neighbor information MUST be sent
within each interval of length REFRESH_INTERVAL. This neighbor
information MAY, however, be sent in the same or in different HELLO
messages.
11.2. HELLO Message Transmission
HELLO messages are transmitted in the format specified by [RFC5444].
11.2.1. HELLO Message Jitter
HELLO messages MAY be sent using periodic message generation or
externally triggered message generation. If using data link and
physical layers that are subject to packet loss due to collisions,
HELLO messages SHOULD be jittered as described in [RFC5148].
Internally triggered message generation (such as due to a change in
local interfaces) MAY be treated as if externally generated message
generation or MAY be not jittered.
HELLO messages MUST NOT be forwarded, and thus message forwarding
jitter does not apply to HELLO messages.

Each form of jitter described in [RFC5148] requires a parameter
MAXJITTER. These interface parameters may be dynamic and are
specified by:
o For periodic message generation: HP_MAXJITTER.
o For externally triggered message generation: HT_MAXJITTER.
When HELLO message generation is delayed in order that a HELLO
message is not sent within HELLO_MIN_INTERVAL of the previous HELLO
message on the same MANET interface, then HELLO_MIN_INTERVAL SHOULD
be reduced by jitter, with maximum reduction HP_MAXJITTER, as
described in [RFC5148]. In this case, HP_MAXJITTER MUST NOT be
greater than HELLO_MIN_INTERVAL.